Method for fabricating inductors with deposition-induced magnetically-anisotropic cores

ABSTRACT

A method of fabricating an inductor includes (a) forming a ferromagnetic core on a semiconductor substrate, the ferromagnetic core lying in a core plane and (b) fabricating an inductor coil that winds around the ferromagnetic core, the inductor coil configured to generate an inductor magnetic field that passes through the ferromagnetic core in a first direction parallel to the core plane. While forming the ferromagnetic core, the method further includes (1) generating a bias magnetic field that passes through the ferromagnetic core in a second direction that is orthogonal to the first direction, and (2) inducing a magnetic anisotropy in the ferromagnetic core with the bias magnetic field.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 15/911,778, titled “Apparatus and Methods for Magnetic CoreInductors with Biased Permeability,” filed on Mar. 5, 2018, which is acontinuation-in-part of U.S. patent application Ser. No. 15/255,804,titled “Apparatus and Methods for Magnetic Core Inductors with BiasedPermeability,” filed on Sep. 2, 2016, which is a continuation of U.S.patent application Ser. No. 14/746,994, titled “Apparatus and Methodsfor Magnetic Core Inductors with Biased Permeability,” filed on Jun. 23,2015, now U.S. Pat. No. 9,991,040, which claims priority to U.S.Provisional Application No. 62/015,726, titled “Apparatus and Methodsfor Magnetic Core Inductors with Biased Permeability,” filed on Jun. 23,2014, each of which is hereby incorporated by reference.

TECHNICAL FIELD

This application is directed to inductive elements comprisinganisotropic media, means for magnetically biasing thereof and methods ofmanufacture and operation for use in applications such asmicroelectronics.

BACKGROUND

The increase in computing power, spatial densities in semiconductorbased devices and energy efficiency of the same allow for ever moreefficient and small microelectronic sensors, processors and othermachines. These have found wide use in mobile and wireless applicationsand other industrial, military, medical and consumer products.

Even though computing energy efficiency is improving over time, thetotal amount of energy used by computers of all types is on the rise.Hence, there is a need for even greater energy efficiency. Most effortsto improve the energy efficiency of microelectronic devices have been atthe chip and transistor level, including with respect to transistor gatewidth. However, these methods are limited and other approaches arenecessary to increase device density, processing power and to reducepower consumption and heat generation in the same.

One field that can benefit from the above improvements is in switchedinductor power conversion devices. Power supplies include powerconverters that convert one form of electrical energy to another. Aregulated power supply is one that controls the output voltage orcurrent to a specific value; the controlled value is held nearlyconstant despite variations in either load current or the voltagesupplied by the power supply's energy source.

Power converters for electronic devices can be broadly divided intoAC-AC, AC-DC and DC-DC power converters. Each of these classes usesimilar devices, techniques and topologies as the others. Modernintegrated circuits using advanced CMOS technology will run on powersupplies with voltages at 1V-DC or less, while the power levelsdelivered to a computer are typically at 120V-AC or higher. The 120V-ACis provided by the grid, where the 120V-AC is derived using AC-ACconverters from much higher voltage levels for power transmission. Oncedelivered to the computer, the 120V-AC power is down-converted in thecomputer to 1V-DC for the microprocessor through a series of powerconverters, AC-DC converters will generally provide a range of DCvoltages such as 3.3V, 5V and 12V, and then a buck converter will takeone of those power levels and down-convert to the 1V-DC required by themicroprocessor.

AC-AC, AC-DC and DC-DC converters can be further divided intoline-frequency (also called “conventional” or “linear”) and switchingpower supplies. Conventional AC-AC and AC-DC power supplies are usuallya relatively simple design, but they become increasingly bulky and heavyfor high-current equipment. This is due to the need for largemains-frequency transformers and heat-sinked electronic regulationcircuitry. Conventional DC-DC converter, linear voltage regulators,produce regulated output voltage by means of an active voltage dividerthat consumes energy, thus making efficiency low.

A switched-mode power supply of the same rating as a conventional powersupply maintains a smaller footprint with better efficiency but at theexpense of being more complex. In an AC-AC switched-mode power supply(SMPS), the AC mains input is directly rectified and then filtered toobtain a DC voltage. The resulting DC voltage is then switched on andoff at a high frequency by electronic switching circuitry, thusproducing an AC current that will pass through a high-frequencytransformer or inductor. In a DC-DC SMPS, a DC input voltage is switchedon and off at a high frequency by electronic switching circuitry andthen passed through a transformer or inductor, where the output of thetransformer or inductor is connected to a decoupling capacitor. Theoutput of the inductor or transformer is the converted DC power supply.

Switching occurs at a very high frequency (typically 10 kHz-500 MHz),thereby enabling the use of transformers and filter capacitors that aremuch smaller, lighter, and less expensive than those found in linearpower supplies operating at mains frequency.

Switched-mode power supplies are usually regulated, and to keep theoutput voltage constant, the power supply employs a feedback controllerthat monitors current drawn by the load. The switching duty cycleincreases as power output requirements increase which puts increasingdemands on the constituent components, particularly the inductors.Switch-mode power supplies also use filters or additional switchingstages to improve the waveform of the current taken from the input powersource. This adds to the circuit complexity, with the inclusion ofadditional inductors and capacitors.

Additionally, the delivery of low voltage/high current power is alsochallenging because power loss increases with higher currents, asfollows:P_(loss)=I²Rwhere, P_(loss) is the power loss over the length of wire and circuittrace, I is the current and R is the inherent resistance over the lengthof wire and circuit trace. As such, and to increase overall performance,there has been a recognized need in the art for large scale integrationof compact and dense electrical components at the chip level, such as,for use with the fabrication of complementary metal oxide semiconductors(CMOS).

With the development of highly integrated electronic systems thatconsume large amounts of electricity in very small areas, the needarises for new technologies which enable improved energy efficiency andpower management for future integrated systems. Integrated powerconversion is a promising potential solution as power can be deliveredto integrated circuits at higher voltage levels and lower currentlevels. That is, integrated power conversion allows for step downvoltage converters to be disposed in close proximity to transistorelements.

Unfortunately, practical integrated inductors that are capable ofefficiently carrying large current levels for switched-inductor powerconversion are not available. Specifically, inductors that arecharacterized by high inductance (>1 nH), low resistance (<1 Ohm), highmaximum current rating (>100 mA), and high frequency response whereby noinductance decrease for alternating current (AC) input signal greaterthan 1 MHz are unavailable or impractical using present technologies.

Furthermore, all of these properties must be economically achieved in asmall area, typically less than 1 mm², a form required for CMOSintegration either monolithically or by 3D or 2.5D chip stacking. Thus,an inductor with the aforementioned properties is necessary in order toimplement integrated power conversion with high energy efficiency andlow output voltage ripple which engenders periodic noise in the outputof the converter's output.

The use of high permeability, low coercivity material is typicallyrequired to achieve the desired properties on a small scale. Inelectromagnetism, permeability is the measure of the ability of amaterial to support the formation of a magnetic field within itself. Inother words, it is the degree of magnetization that a material obtainsin response to an applied magnetic field. A high permeability denotes amaterial achieving a high level of magnetization for a small appliedmagnetic field.

Coercivity, also called the coercive field or force, is a measure of aferromagnetic or ferroelectric material to withstand an externalmagnetic or electric field. Coercivity is the measure of hysteresisobserved in the relationship between applied magnetic field andmagnetization. The coercivity is defined as the applied magnetic fieldstrength necessary to reduce the magnetization to zero after themagnetization of the sample has reached saturation. Thus coercivitymeasures the resistance of a ferromagnetic material to becomingdemagnetized. Ferromagnetic materials with high coercivity are calledmagnetically hard materials, and are used to make permanent magnets.

Coercivity is determined by measuring the width of the hysteresis loopobserved in the relationship between applied magnetic field andmagnetization. Hysteresis is the dependence of a system not only on itscurrent environment but also on its past environment. This dependencearises because the system can be in more than one internal state. Whenan external magnetic field is applied to a ferromagnet such as iron, theatomic dipoles align themselves with it. Even when the field is removed,part of the alignment will be retained: the material has becomemagnetized. Once magnetized, the magnet will stay magnetizedindefinitely. To demagnetize it requires heat or a magnetic field in theopposite direction.

High quality inductors are typically made from high permeability, lowcoercivity material. However, high permeability materials tend tosaturate when biased by a large direct current (DC) magnetic field.Magnetic saturation can have adverse effects as it results in reducedpermeability and consequently reduced inductance.

Soft ferromagnetic materials have a number of useful applications withincircuits and microelectronic applications. High permeability and lowcoercivity are two properties that are useful for enhancing inductance.Inductance is a physical phenomenon that can be explained by thecombination of Oersted's law (an electric current in a conductor createsa proportional magnetic field) and Faraday's law (a time varyingmagnetic flux induces an electric potential in nearby conductors). Theconsequence of inductance is that a change in electric current through aconductor will result in an induced electric potential (EMF) thatresists the change in current. Soft magnetic materials exhibit a highpermeability and consequently can be placed proximal to conductorswithin the path of magnetic fields that originate from these conductors,in order increase inductance values.

Typically, within the plane of the film there exists a hard axis ofmagnetization and an easy axis of magnetization. Along the easy axis,the material tends to exhibit greater coercivity and a highly non-linearrelationship between applied magnetic field and magnetization. Along thehard axis, the material tends to exhibit lower coercivity and arelatively linear relationship between applied magnetic field andmagnetization.

FIG. 1 illustrates a top view of a toroidal inductor 10 according to theprior art. The inductor 10 includes an annular magnetic core 110 and aninductor coil 120. The coil 120 wraps around the core 110 and extends ina circular direction with respect a core plane 125 that bisects the core110. The inductor 10 generates a closed loop magnetic field 140 parallelto the circular direction of the core. As illustrated, the magneticfield 140 induces the core 110 to form a hard axis 150 and an easy axis160 in the plane 125, with the hard axis 150 orthogonal to the easy axis160. Thus, the magnetic field 140 passes through about half the core 110in general alignment with the hard axis 150 and about half the core 110in general alignment with the easy axis 160. This is undesirable becausethe easy axis 160 of the core has a greater coercivity (and thusnon-linearity), which results in magnetic saturation as discussed above.

Accordingly, there is a need for high quality inductors to be used inlarge scale CMOS integration. This provides a platform for theadvancement of systems comprising highly granular dynamic voltage andfrequency scaling as well as augmented energy efficiency. The presentdisclosure contemplates the novel fabrication of efficient and compacton-chip inductors and practical methods for manufacturing operatingthereof for remedying these and/or other associated problems.

SUMMARY

The following description and drawings set forth certain illustrativeimplementations of the disclosure in detail, which are indicative ofseveral exemplary ways in which the various principles of the disclosuremay be carried out. The illustrative examples, however, are notexhaustive of the many possible embodiments of the disclosure. Otherobjects, advantages and novel features of the disclosure will be setforth in the following detailed description of the disclosure whenconsidered in conjunction with the drawings.

As mentioned above, the present invention relates to new and improvedmethods and apparatus for providing integrated inductive elementscomprising anisotropic media and means for magnetically biasing thereof.In particular, inductive devices with magnetic cores utilize biasingcoils for control of core permeability to be used on-chip inmicroelectronic applications. Application of an electrical currentthrough the bias coils generates magnetic fields that bias the magneticmaterials such that a desirable orientation of anisotropy is achievedthroughout the magnetic core and enables modulation of the inductiveresponse of the device.

As described, soft ferromagnetic materials generally exhibit a highpermeability and a low coercivity. Permeability is the relationshipbetween applied magnetic field and magnetization of the material, wherea high permeability suggests the material achieves a high level ofmagnetization for a small magnetic field. Coercivity is the measure ofhysteresis observed in the B-H loop (the relationship between appliedmagnetic field and magnetization) and is the magnetic field required toreduce the magnetization to zero after reaching magnetic saturation.Magnetic saturation is the asymptotic point where any increase in theapplied magnetic field cannot appreciably increase the magnetizationfurther.

Soft ferromagnetic materials have a number of useful applications withincircuits and microelectronic applications. High permeability and lowcoercivity are two properties that are useful for enhancing inductance.Inductance is a physical phenomenon that can be explained by thecombination of Oersted's law (an electric current in a conductor createsa proportional magnetic field) and Faraday's law (a time varyingmagnetic flux induces an electric potential in nearby conductors). Theconsequence of inductance is that a change in electric current through aconductor will result in an induced electric potential (EMF) thatresists the change in current. Soft magnetic materials exhibit a highpermeability and consequently can be placed proximal to conductorswithin the path of magnetic fields that originate from these conductors,in order increase inductance values.

According to one aspect of the invention, the soft magnetic materialscomprise alloys containing at least one of Co, Ni or Fe and/oranisotropic in their magnetic response. Typically, within the plane ofthe film there exists a hard axis of magnetization and an easy axis ofmagnetization. Along the easy axis, the material tends to exhibitgreater coercivity and a highly non-linear relationship between appliedmagnetic field and magnetization. Along the hard axis, the materialtends to exhibit lower coercivity and a relatively linear relationshipbetween applied magnetic field and magnetization.

According to another aspect of the invention, it is desirable to utilizethe hard axis for most applications, due to the low coercivity andlinearity in magnetization. In the case of an inductor, this wouldinvolve aligning the orientation of the hard axis with the expectedorientation of some or all of the magnetic field lines that originatefrom the inductor coil. The orientation of the induced magneticanisotropy may be controlled by several, potentially competing physicalphenomena.

According to one aspect of the invention, the induced anisotropy may beset by controlling the direction of film growth during film depositionand/or by applying a magnetic field during film deposition. According toanother aspect, the induced anisotropy is controlled by applying amagnetic field during a high temperature (greater than 100 degreesCelsius) anneal. Shape anisotropy results from the demagnetizing fieldsof a magnetic structure which are determined by the magnetic structure'sphysical shape.

Other factors can influence a magnetic structures orientation ofanisotropy, including various types of coupling to adjacent magneticstructures. The apparent orientation of anisotropy for a specificstructure is determined by the collection of these effects. According toanother aspect, the application of a static magnetic field sufficientlylarge in magnitude has a similar effect as controlling the orientationof anisotropy by magnetizing the material such that the easy axis alignswith the applied magnetic field.

Another aspect of the invention is directed to a method of fabricatingan inductor, the method comprising: forming a ferromagnetic core on asemiconductor substrate, the ferromagnetic core lying in a core plane;fabricating an inductor coil that winds around the ferromagnetic core,the inductor coil configured to generate an inductor magnetic field thatpasses through the ferromagnetic core in a first direction parallel tothe core plane; and while forming the ferromagnetic core: generating abias magnetic field that passes through the magnetic core in a seconddirection that is orthogonal to the first direction; and inducing amagnetic anisotropy in the ferromagnetic core with the bias magneticfield.

In one or more embodiments, forming the ferromagnetic core comprises:depositing a ferromagnetic material on the semiconductor substrate; andwhile depositing the ferromagnetic material: generating the biasmagnetic field; and inducing the magnetic anisotropy in theferromagnetic material with the bias magnetic field. In one or moreembodiments, forming the ferromagnetic core further comprises defining apattern in the ferromagnetic material. In one or more embodiments,inducing the magnetic anisotropy comprises, with the bias magneticfield, inducing an easy axis of magnetization in the ferromagneticmaterial, the easy axis parallel to the second direction. In one or moreembodiments, inducing the magnetic anisotropy further comprises inducinga hard axis of magnetization in the ferromagnetic material, the hardaxis orthogonal to the easy axis. In one or more embodiments, the hardaxis is parallel to the first direction.

In one or more embodiments, the method further comprises applyingcurrent in a bias coil disposed on the substrate to generate the biasmagnetic field. In one or more embodiments, the method further comprisesapplying at least 10 mA of current in the bias coil. In one or moreembodiments, the method further comprises fabricating the bias coil onthe substrate, the bias coil disposed parallel to the core plane. In oneor more embodiments, the method further comprises disposing the biascoil between the ferromagnetic core and the substrate. In one or moreembodiments, the method further comprises disposing the bias coilbetween the inductor coil and the substrate. In one or more embodiments,the inductor coil includes a top conductor, a bottom conductor, and aVIA that is electrically coupled to the top and bottom conductors, andthe method further comprises disposing the bias coil between theferromagnetic core and the bottom conductor. In one or more embodiments,the method further comprises aligning an axis of symmetry of the biascoil with a target axis of symmetry of the ferromagnetic core.

In one or more embodiments, the ferromagnetic core is formed on a firstsemiconductor substrate and the method further comprises: providingrelative movement between the first semiconductor substrate and a secondsubstrate having a bias coil disposed thereon such that the bias coil onthe second substrate and a target location for the ferromagnetic core onthe first semiconductor substrate are within a predetermined distance ofone another; and generating the bias magnetic field with the bias coil.In one or more embodiments, the method further comprises applyingcurrent in the bias coil to generate the bias magnetic field. In one ormore embodiments, the method further comprises applying at least 10 mAof current in the bias coil.

In one or more embodiments, the relative movement between the firstsemiconductor substrate and the second substrate results in a relativepositioning thereof in which the first semiconductor substrate and thesecond substrate are in contact with one another. In one or moreembodiments, the relative movement between the first substrate and thesecond substrate aligns the bias coil and a target location for theferromagnetic core.

Yet another aspect of the invention is directed to a method offabricating an inductor, the method comprising: forming a ferromagneticcore on a semiconductor substrate, the ferromagnetic core lying in acore plane; fabricating an inductor coil that winds around theferromagnetic core, the inductor coil configured to generate an inductormagnetic field that passes through the ferromagnetic core in a firstdirection parallel to the core plane; and while forming theferromagnetic core: with a bias permanent magnet, producing a biasmagnetic field that passes through the magnetic core in a seconddirection that is orthogonal to the first direction; and inducing amagnetic anisotropy in the ferromagnetic core with the bias magneticfield.

In one or more embodiments, the method further comprises forming thebias permanent magnet on the semiconductor substrate. In one or moreembodiments, the method further comprises disposing the bias permanentmagnet between the ferromagnetic core and the semiconductor substrate.In one or more embodiments, the method further comprises disposing thebias permanent magnet between the inductor coil and the semiconductorsubstrate. In one or more embodiments, the inductor coil includes a topconductor, a bottom conductor, and a VIA that is electrically coupled tothe top and bottom conductors, and the method further comprisesdisposing the bias permanent magnet between the ferromagnetic core andthe bottom conductor.

In one or more embodiments, the method further comprises aligning anaxis of symmetry of the bias permanent magnet with a target axis ofsymmetry of the ferromagnetic core. In one or more embodiments, theferromagnetic core is formed on a first semiconductor substrate and themethod further comprises: providing relative movement between the firstsemiconductor substrate and a second substrate having the bias permanentmagnet disposed thereon such that the bias permanent magnet on thesecond substrate and a target location for the ferromagnetic core on thefirst semiconductor substrate are within a predetermined distance of oneanother; and generating the bias magnetic field with the bias permanentmagnet. In one or more embodiments, the method further comprises formingthe bias permanent magnet on the second substrate. In one or moreembodiments, the relative movement between the first substrate and thesecond substrate results in a relative positioning thereof in which thefirst semiconductor substrate and the second substrate are in contactwith one another. In one or more embodiments, the relative movementbetween the first semiconductor substrate and the second substratealigns the bias coil and the target location for the ferromagnetic core.

In one or more embodiments, forming the ferromagnetic core comprises:depositing a ferromagnetic material on the semiconductor substrate; andwhile depositing the ferromagnetic material: producing the bias magneticfield; and inducing the magnetic anisotropy in the ferromagneticmaterial with the bias magnetic field. In one or more embodiments,forming the ferromagnetic core further comprises defining a pattern inthe ferromagnetic material. In one or more embodiments, the methodfurther comprises placing a shadow mask on the semiconductor substrate,the shadow mask comprising the bias permanent magnet; and depositing theferromagnetic material on the shadow mask, the shadow mask defining thepattern in the ferromagnetic material.

In one or more embodiments, forming the ferromagnetic core furthercomprises, with the bias magnetic field, inducing an easy axis ofmagnetization in the ferromagnetic material, the easy axis parallel tothe second direction. In one or more embodiments, forming theferromagnetic core further comprises inducing a hard axis ofmagnetization in the ferromagnetic material, the hard axis orthogonal tothe easy axis. In one or more embodiments, the hard axis is parallel tothe first direction.

Another aspect of the invention is directed to a method of fabricating aplanar magnetic core, the method comprising: depositing a ferromagneticmaterial on a semiconductor substrate; and while depositing theferromagnetic material: generating a bias magnetic field that passesthrough the magnetic ferromagnetic material in a first direction; andinducing a magnetic anisotropy in the ferromagnetic material, with thebias magnetic field; and defining a pattern in the ferromagneticmaterial to form the planar magnetic core, the planar magnetic corehaving the magnetic anisotropy.

In one or more embodiments, inducing the magnetic anisotropy comprisesinducing an easy axis of magnetization in the ferromagnetic material,the easy axis parallel to the first direction. In one or moreembodiments, inducing the magnetic anisotropy further comprises inducinga hard axis of magnetization in the ferromagnetic material, the hardaxis orthogonal to the easy axis.

In one or more embodiments, the method further comprises placing ashadow mask on the semiconductor substrate, the shadow mask comprisingthe bias permanent magnet; and depositing the ferromagnetic material onthe shadow mask, the shadow mask defining the pattern in theferromagnetic material.

In the Drawings

FIG. 1 illustrates a top view of a toroidal inductor according to theprior art.

FIG. 2 illustrates an isometric perspective of an elementary inductorwith an anisotropic magnetic core;

FIG. 3 depicts an isometric perspective of an exemplary magnetic corewith a biasing coil according to an alternate embodiment;

FIG. 4 illustrates a top-down view of an exemplary magnetic core withbiasing coil;

FIG. 5A illustrates a top-down view of an exemplary toroidal inductorwith anisotropic magnetic core and integrated biasing coil;

FIG. 5B illustrates another top-down view of the toroidal inductor ofFIG. 5A;

FIG. 6 portrays a side-view of an exemplary toroidal inductor withanisotropic magnetic core and integrated biasing coil;

FIG. 7 depicts a top-view of an exemplary toroidal mutual inductor withanisotropic magnetic core and integrated biasing coil;

FIG. 8 depicts a top-view of an exemplary race-track mutual inductorwith anisotropic magnetic core and integrated biasing coil;

FIG. 9 depicts a top-view of an exemplary rectangular mutual inductorwith anisotropic magnetic core and integrated biasing coil;

FIG. 10 graphically illustrates the juxtaposition of hysteresis loopsfor the hard and soft axes in a soft ferromagnetic material;

FIG. 11 is a graphical abstraction of a magnetic anisotropic inductorbelow a saturation current condition;

FIG. 12 is a graphical abstraction of a magnetic anisotropic inductorabove a saturation current condition;

FIG. 13 is a graphical abstraction that illustrates the saturationcurrent increasing over time as the bias coil current increases;

FIG. 14 is a graphical abstraction that illustrates the saturationcurrent increasing over time as the inductor coil current increases;

FIG. 15 is a flow chart of a method for operating an inductor assembly

FIG. 16 portrays a side-view of an exemplary toroidal inductor withanisotropic magnetic core and integrated biasing coil disposed on asubstrate, in accordance with at least some embodiments;

FIG. 17 portrays a side view of an exemplary toroidal inductor withanisotropic magnetic core on a first substrate and a side view of abiasing coil disposed on a second substrate, in accordance with at leastsome embodiments;

FIG. 18 is a flowchart of a method, in accordance with at least someembodiments;

FIG. 19 portrays a side view of an exemplary toroidal inductor withanisotropic magnetic core on a first substrate and a side view of abiasing coil disposed on a second substrate, in accordance with at leastsome embodiments;

FIG. 20 portrays a side view of an exemplary toroidal inductor withanisotropic magnetic core on a first substrate and a side view of abiasing coil disposed on a second substrate, in accordance with at leastsome embodiments;

FIG. 21 is a flow chart of a method for fabricating an inductor having adeposition-induced magnetic anisotropy according to one or moreembodiments;

FIG. 22 is a flow chart of a method for forming a deposition-inducedanisotropic magnetic core according to one or more embodiments;

FIG. 23 is a cross-sectional view of a semiconductor structure toillustrate a first step for fabricating an inductor that includes adeposition-induced anisotropic magnetic core according to one or moreembodiments;

FIG. 24 is a cross-sectional view of a semiconductor structure toillustrate a second step for fabricating an inductor that includes adeposition-induced anisotropic magnetic core according to one or moreembodiments;

FIGS. 25 and 26 are cross-sectional views of a semiconductor structureto illustrate a third step for fabricating an inductor that includes adeposition-induced anisotropic magnetic core according to one or moreembodiments;

FIG. 27 is a cross-sectional view of a semiconductor structure toillustrate a fourth step for fabricating an inductor that includes adeposition-induced anisotropic magnetic core according to one or moreembodiments;

FIG. 28 is a cross-sectional view of a semiconductor structure toillustrate a fifth step for fabricating an inductor that includes adeposition-induced anisotropic magnetic core according to one or moreembodiments;

FIG. 29 is a flow chart of a method for fabricating an inductor thatincludes a deposition-induced anisotropic magnetic core according to oneor more embodiments;

FIGS. 30 and 31 are cross-sectional views of a semiconductor structureto illustrate an alternative embodiment for fabricating an inductor thatincludes a deposition-induced anisotropic magnetic core;

FIG. 32 is a flow chart of a method for fabricating an inductor thatincludes a deposition-induced anisotropic magnetic core according to analternative embodiment;

FIG. 33 is a cross-sectional view of an assembly to illustrate anotheralternative embodiment for fabricating an inductor that includes adeposition-induced anisotropic magnetic core;

FIG. 34 is a cross-sectional view of a fully-fabricated semiconductorstructure including an inductor that includes the deposition-inducedanisotropic magnetic core formed in FIG. 33;

FIG. 35 is a flow chart of a method for fabricating an inductor thatincludes a deposition-induced anisotropic magnetic core according to analternative embodiments;

FIG. 36 is a cross-sectional view of an assembly to illustrate yetanother alternative embodiment for fabricating an inductor that includesa deposition-induced anisotropic magnetic core;

FIG. 37 is a cross-sectional view of an assembly 3700 to illustrateanother alternative embodiment for fabricating an inductor that includesa deposition-induced anisotropic magnetic core;

FIG. 38 is a cross-sectional view of an assembly 3800 to illustrate yetanother alternative embodiment for fabricating an inductor that includesa deposition-induced anisotropic magnetic core;

FIG. 39 is a flow chart 3900 of a method for fabricating an inductorthat includes a deposition-induced anisotropic magnetic core usingpermanent magnets according to an alternative embodiment;

FIG. 40 is a cross-sectional view of a semiconductor structure thatincludes permanent magnets for forming a deposition-induced anisotropicmagnetic core according to an alternative embodiment; and

FIG. 41 is a cross-sectional view of a semiconductor structure thatincludes permanent magnets for forming a deposition-induced anisotropicmagnetic core according to another alternative embodiment.

DETAILED DESCRIPTION

As mentioned above, the present invention relates to inductive elementsthat utilize anisotropic materials and incorporate secondary biasingcoils for the purpose of biasing the magnetic cores. One or moreembodiments or implementations are hereinafter described in conjunctionwith the drawings, where like reference numerals are used to refer tolike elements throughout, and where the various features are notnecessarily drawn to scale.

The present invention discloses a novel inductor which can be integratedinto large scale chip fabrication, according to one embodiment.Inductance is the property of a conductor by which a change in currentin the conductor “induces” (creates) a voltage (electromotive force) inboth the conductor itself (self-inductance) and in any nearby conductors(mutual inductance). These effects are derived from two fundamentalobservations of physics: first, that a steady current creates a steadymagnetic field (Oersted's law), and second, that a time-varying magneticfield induces voltage in nearby conductors (Faraday's law of induction).

To add inductance to a circuit, electrical or electronic componentscalled inductors are used. An inductor, also called a coil or reactor,is a passive two-terminal electrical component that resists changes inelectric current passing through it. It consists of a conductor such asa wire, usually wound into a coil. When a current flows through it,energy is stored temporarily in a magnetic field in the coil. When thecurrent flowing through an inductor changes, the time-varying magneticfield induces a voltage in the conductor, according to Faraday's law ofelectromagnetic induction, which opposes the change in current thatcreated it.

Inductors increase their constituent magnetic fields by way of magneticcores made of iron or ferrite inside the coil. A magnetic core canincrease the inductance of a coil by a factor of several thousand, byincreasing the magnetic field due to its higher magnetic permeability.However, the magnetic properties of the core material cause several sideeffects that alter the behavior of the inductor which are described bythe following and addressed by the present invention.

As discussed, a time-varying current in a ferromagnetic inductorproduces a time-varying magnetic field in its core. Energy losses occurin the core material (core loss) due to magnetic field change which aredissipated as heat. Core losses arise in the based two conditions: eddycurrents and hysteresis. A changing magnetic field induces circulatingloops of electric current in the conductive metal core. The currentsdissipate into heat as a function of any nominal resistance associatedwith core material. The amount of energy loss is proportional to thearea inside the loop of current.

Changing or reversing the magnetic field in the core also causes lossesdue to the motion of the tiny magnetic domains it is composed of. Theenergy loss is proportional to the area of the hysteresis loop in the BHgraph of the core material. Materials with low coercivity have narrowhysteresis loops and corresponding low hysteresis losses. Energy lossper cycle of alternating current is constant. As such, core lossesincrease linearly with frequency.

Another concern addressed by the present invention is a condition ofnonlinearity. High currents in a ferromagnetic core coil producesmagnetic core saturation. Observed in ferromagnetic materials (e.g.,iron, nickel, cobalt and alloys thereof), saturation is the statereached when an increase in applied external magnetic field H cannotappreciably increase the magnetization of the material further, so thetotal magnetic flux density B levels off.

In a saturated state, the inductance does not remain constant butchanges with the current through the device. This is called nonlinearityand results in distortion of the signal. Even in an unsaturated state,materials exhibiting high coercivity produce signal distortion due tothe nature of hysteretic loop, as the gain is a function of thenon-linear shape of the curve.

The present invention employs magnetically anisotropic material—andmanipulation thereof—to overcome some of the described shortcomings.Magnetic anisotropy is the directional dependence of a material'smagnetic properties. In the absence of an applied magnetic field, amagnetically isotropic material has no preferential direction for itsmagnetic moment while a magnetically anisotropic material will align itsmoment with one of the easy axes. An easy axis is an energeticallyfavorable direction of spontaneous magnetization that is determined bythe sources of magnetic anisotropy. The two opposite directions along aneasy axis are usually equivalent, and the actual direction ofmagnetization can be along either of them.

In one or more non-limiting embodiments, magnetic materials withuniaxial anisotropy are disclosed including Co, Fe, Ni, and anycombination of these elements, potentially with other non-magneticmaterials such as Ta, Zr, B, and P. Uniaxial anisotropic materials haveone easy axis. Generally orthogonal to the easy axis, hard axes (not tobe confused with “hard” ferromagnetic materials which denotes largecoercivity) are desired for inductance. Hard axes are easily magnetizedbut tend not to hold their magnetization making them suitable forinductor core materials. Although the easy axis is more easilymagnetized, by definition, hard axes retain significant permeabilitiesand linear operation beneath saturation. Other embodiments pertaining tocrystallography, anisotropic orientation and saturation control will bediscussed in greater detail later in the disclosure. In someembodiments, the magnetic anisotropy is induced during deposition of theinductor core material(s).

FIG. 2 illustrates an isometric perspective of an elementary inductor 20with an anisotropic magnetic core 210. Anisotropic magnetic core 210lies in a core plane 225. The core 210 is oriented such that its hardaxis 265 is parallel to the core plane 225. That is, one or more (foruniaxial) hard axes 225 are disposed along and/or parallel with the(+/−) z direction. The hard axis 265 of a magnetic anisotropic materialexhibits properties of soft ferromagnetic materials. The core 210 can beformed of Co, Ni or Fe or an alloy of one or more of such elements.

Soft ferromagnetic materials have a number of useful applications withincircuits and microelectronic applications. They demonstrate relativelyhigh permeability, low coercivity and linearity; three properties thatare useful for enhancing inductance. Low coercivity mitigates corelosses that are incurred by repeatedly changing the magnetization of themagnetic material. Methods and techniques are described to ensure thatthe high permeability and low coercivity of the material are maintainedover specific ranges of inductor current, frequency and applied magneticfield strengths.

Soft ferromagnetic can be placed proximal to conductors in order toincrease inductance values. In the present embodiment, anisotropicmagnetic core 210 is disposed within and magnetically coupled to a coil220, which is composed of one or more layers of electrical conductor(e.g., copper), in order to provide a high quality inductance with lowresistance through the conductive element. Inductor 20 further comprisesterminals 213, 214 which are conductive elements for the purpose ofelectrical communication to other devices or circuits within thesemiconductor device.

In one aspect, anisotropic materials are integrated with otherelectronic circuits on a single, or multiple semiconductor substrates,in order to improve inductance or provide additional functionality thatwould not otherwise be available on an integrated circuit. Specifically,the integration of anisotropic magnetic cores enables efficient switchedinductor power conversion.

The hard axis 265 can be oriented during the formation of the core 210and/or it can be induced during operation by a magnetic field Hgenerated by a bias coil. Various embodiments of forming and/or inducingthe hard axis 265 are described herein.

In operation, a current flows through the conductive coil 220, which iswrapped around the core 220. The coil 220 extends in a direction 255parallel to the core plane 225. The current flowing through the coil 220induces a magnetic field H that travels parallel to the direction 255 ofwinding and, thus, in alignment with the hard axis 265 for the length ofthe magnetic core 220. Outside of the magnetic core, the inducedmagnetic flux forms a closed loop as described by Gauss's law formagnetism.

In some embodiments, the hard axis 265 can be induced during operationof the inductor 20. For example, a second magnetic field 270 can begenerated in a direction orthogonal to the core plane 225 or orthogonalto the magnetic field that is generated by the inductor coil. Oneskilled in the art will recognize that at least in some embodiments, thecore plane 225 is parallel with the magnetic field generated by theinductor coil for the length of the magnetic core 220, as describedabove. The second magnetic field 270 induces an easy axis in the core210 in a direction parallel to the second magnetic field 270. The hardaxis 265 naturally aligns in an orthogonal direction to the easy axisand, thus, will be induced to align in a direction parallel to the coreplane 225 and/or the direction of the magnetic field for the length ofthe magnetic core 220. The second magnetic field 270 can be generated bya bias coil or any other method as understood by those skilled in theart. The easy axis and hard axis can be disposed in the same plane.

The core 210 can be in the form a variety of shapes. For example, thecore 210 can curve into a shape with a circular cross section such asdescribed below. The core 210 can also be elongated (e.g., aparallelepiped).

In some embodiments, the core 210 can be manufactured while an externalmagnetic field 270′ is applied in the direction of the y-axis, as shownin FIG. 2. The application assures coaxial alignment with theanisotropy's easy axis. This effectively orients the anisotropy's hardaxis to be coupled to the inductor's magnetic field H in operation,thereby engendering the desired characteristics of low coercivity,relatively high permeability and linearity. In such embodiments a biasmagnetic field is not needed during operation to assure alignment of thehard axis with the inductor's magnetic field. However, for thin magneticfilms, shape anisotropy may be large enough to preclude to formation ofthe easy axis of magnetization orthogonal to the core plane or thedirection of the magnetic field for the length of the magnetic core 220.

The induced magnetic anisotropy may be controlled by several,potentially competing physical phenomena: magnetocrystalline anisotropy,shape anisotropy, magnetoelastic anisotropy and exchange anisotropy.Arising from spin-orbit coupling, the atomic structure of a crystalintroduces preferential directions for the magnetization inmagnetocrystalline anisotropy. In one or more embodiments, the inducedanisotropy may be set by controlling the direction of crystal latticegrowth during deposition by applying the magnetic field 270′ to a seedlayer or substrate. In other embodiments, the magnetic field 270′ isapplied after the core is deposited during a high temperature anneal. Inthe high-temperature anneal, the magnetic field strength should beconsiderably higher than the magnetic material's intrinsic saturationfield (e.g., greater than or equal to about 30 Oe), the temperatureshould be greater than 200° C. and the duration of the anneal should beseveral hours. Many combinations of temperature, magnetic field strengthand time may be effective at inducing the magnetic anisotropy. This isuseful in more amorphous and sintered magnetic core materials.

Shape anisotropy occurs as a result of orientation of magnetic domainsin an effort to minimize their cumulative field energy. Magnetic domainsalign their moments to effectively demagnetize each othermacroscopically. Shape anisotropy is a function of magnetic structure,which is determined by the magnet's physical scale, shape, symmetry andmaterial. Other factors can influence a magnetic structures orientationof anisotropy, including various types of coupling to adjacent magneticstructures.

The apparent orientation of anisotropy for a specific structure isdetermined by the collection of these effects. The application of astatic magnetic field sufficiently large in magnitude has a similareffect as controlling the orientation of anisotropy, by magnetizing thematerial such that the easy axis aligns with the applied magnetic fieldthereby allowing microcrystalline anisotropy to dominate. The magnitudeof the static magnetic field should be on the order of the magnitude ofthe saturation field of the magnetic material.

In one or more embodiments, insulating layers in the x-z or y-z planesare employed to suppress the formation of eddy currents and minimizeother loss mechanisms over potential operating conditions. An electricalinsulator is a material whose internal electric charges do not flowfreely. An electrical insulator, therefore, does not conduct an electriccurrent under the influence of an electric field. It is characterized bya low conductivity/high resistivity. Exemplary materials include glass,paper and Teflon, which have high resistivity making them very goodelectrical insulators. The layers included in these magnetic inductorscan be about (i.e., within +/−10%) 1 nm to about 100 nm in thickness.

According to one aspect, anisotropic magnetic core 210 is fabricatedwith magnetic film layers and alternating electrically insulatinglayers. Insulating layers are inserted into the magnetic film layersseparating the film into two or more thin (about 1 nm to about 1000 nm)laminations that are electrically isolated. The insulating layerssuppress the formation of eddy currents, which is a major source of lossat high frequencies. In one or more embodiments, electrically insulatinglayers comprises photoresist, metal oxide, silicon dioxide, polymer orother suitable material suitably used in semiconductor devicefabrication.

FIG. 3 depicts an isometric perspective of an exemplary incompletemagnetically coupled inductor 30 with a bias coil 375 according to anembodiment. In the configuration depicted, anisotropic magnetic core 310is annular in shape and fabricated to be used in a toroidal inductor.Bias coil 375 with terminals 384, 385 is manufactured using anyconductive or semiconductive materials. If integrated into printedcircuit board (PCB) fabrication, these can be circuit traces, wires,strip lines or any other suitable material. One skilled in the art canappreciate the limit to the number of turns N in bias coil 375 is apractical, engineering consideration.

Bias coil 375 is included primarily for the purposes of controlling themagnetic materials orientation of anisotropy. Therefore, it is desirablethat the bias coil 375 consume very little power during operation of thedevice. This can be accomplished by using many turns in the bias coil,so that a small current can induce a magnetic field similar or greaterin magnitude than the inductor coil. It is acceptable for the bias coilto have a large resistance, whereas this is generally not true for theinductor coil where resistance must be kept low to maintain a goodinductor quality factor.

According to one aspect of the invention, a biasing coil 375 is disposedproximal to the anisotropic magnetic core 310 to induce the desiredorientation of anisotropy for the entire length or substantially theentire length of the magnetic flux path. When a DC electrical current ispassed through the biasing coil 375, the biasing magnetic fields 380that originate (DC bias fields) are perpendicular to the magnetic fieldsof the inductor coil (inductor fields not shown). The biasing magneticfield 380 must be large enough in magnitude to steer the easy axis ofmagnetization to orient parallel to the bias field.

At the intersecting plane of biasing magnetic field 380 and anisotropicmagnetic core 310 the field lines of the biasing magnetic field 380 aredisposed radially to the plane of the anisotropic magnetic core 310thereby inducing an easy axis of the same direction. Consequently, thehard axis of magnetization will be oriented tangential to the radialdirection along the inductor fields (depicted later in the disclosure),which will result in a higher permeability for the entire length of theinductor flux/field path and consequently a higher inductance. The easyaxis and the hard axis can be disposed in the same plane.

FIG. 4 illustrates a top-down view of an exemplary incompletemagnetically coupled inductor 40 with biasing coil 475, in accordancewith the present embodiment depicted in FIG. 3. Again, anisotropicmagnetic core 410 is generally annular in shape and fabricated to beused in a toroidal inductor. Biasing coil 475 with terminals 484, 485are manufactured using any conductive or semiconductive materials. Thebiasing coil 475 generates magnetic field lines 480 that radiate in theradial direction in the plane of anisotropic magnetic core 410 therebyinducing anisotropy of the easy axis and consequently the hard axistangentially thereof. The easy and hard axes can be co-planar.

FIG. 5A illustrates a top-down view of an exemplary toroidal inductor 50with anisotropic magnetic core 510 continuing with the presentembodiment. Toroidal inductor 50 comprises integrated biasing coil 575,biasing terminals 584, 585, a toroidal or annular shaped anisotropicmagnetic core 510, inductor coil 520, and inductor terminals 513, 514.Integrated biasing coil 575, biasing terminals 584, 585, and anisotropicmagnetic core 510 are fabricated and disposed in the manner describedabove. The biasing coil 575 wraps in a generally spiral directionparallel to a core plane 525.

Inductor coil 520 wraps around the core 510, which lies in the coreplane 525. The core plane 525 is orthogonal to an axis of symmetry 530,which extends through a center 535 of the core 510. The inductor coil520 wraps in a direction parallel to a core plane 525. The coil 520 canbe manufactured using any conductive material and will be discussed inmore detail later in the disclosure. Inductor terminals 513, 514electrically couple to other circuits and devices integrated intosemiconductor fabrication. Application of a DC current through inductorterminals 513, 514 gives rise to a magnetic field 565 that extendsthrough the core 510 in an arc or closed loop. The magnetic field 565 isorthogonal to the radial direction (e.g., the direction of the biasmagnetic field) and coaxial to the hard axis of the induced magneticanisotropy. The magnetic field 565 is also parallel to the core plane525.

The magnetic field 565 and flux induced by the inductor coil 520 forms aclosed circular path with the magnetic anisotropic core 510.

It is noted that the core 510 can have a generally circular crosssection in the core plane 525. Although a toroidal or annular shape isillustrated in FIG. 5, the core 510 can have other cross sectionalshapes such as a circle, an oval, an ellipse, or similar shapes. Suchcross sectional shapes can form a core 510 having variousthree-dimensional shapes such as a sphere, an ovoid, a spheroid, acylinder, a cone, an ellipsoid, or similar shapes.

FIG. 5B illustrates another top view of the toroidal inductor 50. Asillustrated, the hard axis 550 is induced by the inductor coil 520 tofollow and align with the magnetic field 565. Thus, both the hard axis550 and the magnetic field 550 have a generally circular closed path andextend in an arc parallel to the core plane 525. As discussed above,this is beneficial because the hard axis 550 has a lower coercivity,which results in a reduction or elimination of magnetic saturation.

FIG. 6 portrays a side view of an exemplary toroidal inductor 60comprising anisotropic magnetic core 610, inductor coil 620, andintegrated biasing coil 675. The side view is taken through a planeorthogonal to a core plane 625 (described below). The inductor coil 620includes a top conductor 621, bottom conductor 622 and conductorvertical interconnect access (VIA) 623. The complete device fabricationspans four layers with insulating layers interposed therebetween. VIA623 electrically couples top conductor 621 to bottom conductor 622 inpredetermined locations and is electrically isolated from anisotropicmagnetic core 610. The biasing coil 675 wraps in a generally spiraldirection parallel to the core plane 625.

The inductor coil 620 is wound around the core 610, which lies in thecore plane 625. The core plane 625 is orthogonal to an axis of symmetry630, which extends through a center 635 of the core 610. As illustrated,the inductor coil 620 has a generally rectangular cross section in theplane orthogonal to the core plane 625. It is noted that the inductorcoil 620 can have other generally rectangular shapes in cross section,such as a square, a parallelogram, or a similar shape. Alternatively,the inductor coil 620 can have a generally circular shape in crosssection, such as a circle, an oval, an ellipse, or a similar shape.

In operation, a current in the inductor coil 620 generates a magneticfield that passes through the core 610 in a closed loop parallel to thecore plane 625. The biasing coil 675, which is disposed parallel to thecore plane 625, generates a second magnetic field 680 that passesthrough the core 610 in a second direction (e.g., radially) that isorthogonal to the first direction. As discussed above, the secondmagnetic field 680 induces an easy axis in the core 610 along thedirection of the second magnetic field 680 (i.e., the second or radialdirection), which causes alignment of the hard axis with the magneticfield caused by the inductor coil 620. As discussed above, the easy axisand the hard axis can be co-planar.

In at least some embodiments, the device is fabricated on a substrate.

FIG. 16 portrays a side view of the device disposed on a substrate 1602,in accordance with at least some embodiments.

As with FIG. 6 discussed above, the side view is taken through the coreplane 625.

As used herein, the term “disposed on” means “disposed directly on”and/or “disposed indirectly on.” Unless stated otherwise, the term “on”does not necessarily mean “on top of” since relative position (above orbelow) depends on orientation.

As used herein, the term “substrate” may comprise any type of substrate.In some embodiments, the substrate may include one or more integratedcircuits or portion(s) thereof.

In at least some embodiments, the device may be fabricated without thebiasing coil 675, and a biasing, e.g., biasing coil 675, for use ininducing an orientation of anisotropy for the magnetic core 610 may bedisposed on a second (separate) substrate. In at least some embodiments,this allows a single biasing coil to be used in inducing an orientationof anisotropy for magnetic cores in multiple devices, and as such, mayreduce the cost of each device since each device does not need its own“on board” biasing coil.

FIG. 17 portrays a side view of the device disposed on a firstsubstrate, e.g., substrate 1602, without the biasing coil 675, and aside view of a biasing coil, e.g., biasing coil 675, disposed on asecond substrate 1702, in accordance with at least some embodiments.

As with FIG. 16, the side view is taken through the core plane 625.

In at least some embodiments, the biasing core 675 has a center and/oraxis (of symmetry or otherwise) 1704.

In at least some embodiments, the biasing coil, e.g., biasing coil 675,on the second substrate 1702, may be used in inducing a permanent orsemi-permanent orientation of anisotropy for a magnetic core, e.g.,magnetic core 610, on the first substrate 1602.

FIG. 18 is a flowchart 1800 of a method for using the biasing core,e.g., biasing core 675, disposed on the second substrate 1702 to inducea permanent or semi-permanent orientation of anisotropy for a magneticcore, e.g., magnetic core 610, disposed on the first substrate 1602, inaccordance with at least some embodiments.

Referring to FIG. 18, at 1802, the method may include providing relativemovement between the first substrate 1602 and the second substrate 1702such that the biasing core, e.g., biasing core 675, disposed on thesecond substrate 1702 and the magnetic core, e.g., magnetic core 610,disposed on the first substrate 1602 are within range of one another, inaccordance with some embodiments.

As used herein, the term “within range of one another” means closeenough that the biasing coil can: (i) generate a bias magnetic fieldthat passes through the magnetic core and (ii) generate heat to heat themagnetic core, to induce a permanent or semi-permanent orientation ofanisotropy for the magnetic core.

In at least some embodiments, the relative movement between the firstsubstrate and the second substrate comprises moving the second substratetoward the first substrate, moving the first substrate toward the secondsubstrate and/or a combination thereof.

FIG. 19 portrays a side view of the device disposed on a firstsubstrate, e.g., substrate 1602, without the biasing coil 675, and aside view of a biasing coil, e.g., biasing coil 675, disposed on asecond substrate 1702, after relative movement between the firstsubstrate and the second substrate such that the biasing core disposedon the second substrate 1702 and the magnetic core disposed on the firstsubstrate 1602 are within range of one another, in accordance with atleast some embodiments.

As with FIG. 17, the side view is taken through the core plane 625.

In at least some embodiments, the relative movement between the firstsubstrate and the second substrate result in a relative positioningthereof in which the biasing coil 675 is disposed parallel to the coreplane 625.

In at least some embodiments, the biasing core 675 has a center and/oraxis (of symmetry or otherwise) 1704 and the relative movement betweenthe first substrate and the second substrate result in a relativepositioning thereof in which the center and/or axis 1704 of the biasingcore 675 is aligned with and/or parallel to the center 635 and/or axisof symmetry 630 of the magnetic core 610.

In at least some embodiments, the relative movement between the firstsubstrate, e.g., first substrate 1602, and the second substrate, e.g.,second substrate 1702, result in a relative positioning thereof in whichthe first substrate 1602 and the second substrate 1702 are in contactwith one another.

FIG. 20 portrays a side view of the device disposed on a firstsubstrate, e.g., substrate 1602, without the biasing coil 675, and aside view of a biasing coil, e.g., biasing coil 675, disposed on asecond substrate 1702, with the first substrate in contact with thesecond substrate, in accordance with at least some embodiments.

As with FIG. 19, the side view is taken through the core plane 625.

In at least some embodiments, the first substrate, e.g., first substrate1602, has an outer surface (major or otherwise) 1902 (FIG. 19) and thesecond substrate, e.g., second substrate 1702, has an outer surface(major or otherwise) 1904 (FIG. 19) and the relative movement betweenthe first substrate and the second substrate result in a relativepositioning thereof in which the outer surface 1902 of the firstsubstrate and the outer surface 1904 of the second substrate are incontact with one another. In at least some embodiments, a major portionof the outer surface 1902 of the first substrate and a major portion ofthe outer surface 1904 of the second substrate are in contact with oneanother.

Unless stated otherwise, the term “major portion”means a portion that isgreater than 50%.

In at least some embodiments, the contact comprises uniform contact.

In at least some embodiments, the relative movement between the firstsubstrate and the second substrate result in a relative positioningthereof in which the biasing coil 675 is disposed parallel to the coreplane 625.

In at least some embodiments, the biasing core 675 has a center and/oraxis (of symmetry or otherwise) 1704 and the relative movement betweenthe first substrate and the second substrate result in a relativepositioning thereof in which the center and/or axis 1704 of the biasingcore 610 is aligned with and/or parallel to the center 635 and/or axisof symmetry 630 of the magnetic core 610.

In at least some embodiments, the method may further comprise applyingforce, e.g., force 2010, to press at least one of the second substrateand the first substrate against the other. In at least some embodiments,this comprises applying force to press the second substrate against thefirst substrate, applying force to press the first substrate against thesecond substrate and/or a combination thereof.

Referring again to FIG. 18, at 1804, the method may further includeapplying current in the biasing coil, e.g., biasing coil 675, to: (i)generate a bias magnetic field, e.g., magnetic field 680, that passesthrough the magnetic core, e.g., magnetic core 610, in a seconddirection that is orthogonal to the first direction and (ii) generateheat to heat the magnetic core, to induce a permanent or semi-permanentorientation of anisotropy for the magnetic core.

In at least some embodiments, applying current in the bias coilcomprises applying at least 10 mA of current in the bias coil.

In at least some embodiments, the heat is generated for at least 15minutes.

In at least some embodiments, the generated heat is sufficient to heatthe magnetic core to a temperature greater than 200° C.

In at least some embodiments, said induce a permanent or semi-permanentorientation of anisotropy for the magnetic core comprises induce apermanent orientation of anisotropy for the magnetic core.

In at least some embodiments, said induce a permanent or semi-permanentorientation of anisotropy for the magnetic core comprises permanently orsemi-permanently fix an easy axis of magnetization of the magnetic coreparallel to the second direction.

In at least some embodiments, said permanently or semi-permanently fixan easy axis of magnetization of the magnetic core parallel to thesecond direction causes a hard axis of magnetization of the magneticcore to be permanently or semi-permanently oriented parallel to thefirst direction.

In at least some embodiments, said induce a permanent or semi-permanentorientation of anisotropy for the magnetic core comprises permanentlyfix an easy axis of magnetization of the magnetic core parallel to thesecond direction to cause a hard axis of magnetization of the magneticcore to be permanently oriented parallel to the first direction.

In at least some embodiments, the biasing core 675 may generate a secondmagnetic field 680 that passes through the core 610 in a seconddirection (e.g., radially) that is orthogonal to the first direction andinduces an easy axis in the core 610 along the direction of the secondmagnetic field 680 (i.e., the second or radial direction), which causesalignment of the hard axis with the magnetic field caused by theinductor coil 620. As discussed above, the easy axis and the hard axiscan be co-planar.

FIG. 7 depicts a top-view of an exemplary toroidal mutual inductor 70comprising integrated biasing coil 775, anisotropic magnetic core 710,primary inductor coil 720A and secondary inductor coil 720B. Themagnetic field 765 and flux induced by primary inductor coil 720A formsa closed circular path with the magnetic anisotropic core 710 whichmagnetically couples secondary coil 720B. Electrical communicationoccurs though primary 713, 714 and secondary terminals 63, 69,respectively.

Toroidal mutual inductor 70 can function as a transformer or othercoupled inductor. Primary and secondary coils 720A, 720B wind around thesame magnetic anisotropic core 61. In the present embodiment, windingsare separate (distinct). In another embodiment, windings areinterleaved, at least in part. In another embodiment, the number ofwindings on the primary and secondary turns may be dissimilar to form atransformer with turns ratio other than 1:1.

According to another embodiment, FIG. 8 depicts a top-view of anexemplary race-track mutual inductor 80 comprising integrated biasingcoil 875, anisotropic magnetic core 810, primary inductor coil 820A andsecondary inductor coil 820B. Mutual inductor 80 is in the shape of anelongated toroid or an oval in cross section. As with the previousembodiment, the magnetic field and flux induced by primary inductor coil820A forms a closed elliptical path with the magnetic anisotropic core810 which magnetically couples secondary coil 820B. The biasing coil 875induces a hard axis in the core 810 to align with the magnetic fieldgenerated by the inductor coils 820A, 820B.

According to another embodiment, FIG. 9 depicts a top-view of anexemplary rectangular mutual inductor 90 comprising integrated biasingcoil 975, anisotropic magnetic core 910, primary inductor coil 920A andsecondary inductor coil 920B. The core 910 is substantially rectangularshaped, but other 4-sided profiles, such as square, rhombus, etc., arenot beyond the present invention. As with the previous embodiment, themagnetic field and flux induced by primary inductor coil 920A forms aclosed elliptical path with the magnetic anisotropic core 910 whichmagnetically couples secondary coil 920B. Alignment of the magneticfield generated by the inductor coils 920A, 920B with the hard axis ofthe core 910 is achieved in the same way as described above.

According to another embodiment of a bias coil inductor, a bias coil maybe fabricated using the same conductive interconnect layers as theinductor coil. In another embodiment, the bias coil may be used toinduce the magnetic anisotropy only in locations of the magnetic corewhere the intrinsic hard axis of magnetization of the core is notaligned with the magnetic flux that is generated by the inductor coil.In regions of the magnetic core where the intrinsic hard axisorientation is aligned with the inductor coil's magnetic field, no biasfield is necessary. In regions of the magnetic core where the intrinsichard axis orientation is not aligned with the inductor coil's field, thebias coil can be used to induce a magnetic field that aligns the hardaxis with the magnetic flux originating from the inductor coil.

This invention is also applicable to other inductor topologies anddimensions. Maximum benefit is achieved when the magnetic core forms aclosed path for the inductor fields (this provides maximum inductanceenhancement). However, there is still benefit achieved when a biasingcoil is used with open inductor cores such as solenoids. Further, thisinvention applies to any coupled inductors and transformers, where oneor more electrically isolated coils wrap around the same magnetic core.

FIG. 10 graphically illustrates the juxtaposition of hysteresis loopsfor the hard 1001 and soft axes 1002 in a soft ferromagnetic material.Suitable soft magnetic materials employed in one or more embodimentscomprise alloys containing at least one of Co, Ni or Fe, which areanisotropic in their magnetic response. Magnetic anisotropy is thedirectional dependence of a material's magnetic properties. In theabsence of an applied magnetic field, a magnetically isotropic materialhas no preferential direction for its magnetic moment, while amagnetically anisotropic material will align its moment with one of theeasy axes in the presence of an applied magnetic field.

An easy axis is an energetically favorable direction of spontaneousmagnetization. The two opposite directions along an easy axis areusually equivalent, and the actual direction of magnetization can bealong either of them. Basal plane (two easy axes) and other magneticanisotropy is not beyond the scope of the present invention. However, inpractice these may need to be grown using crystallographic seed layers.

In the context of the present invention, there exists one or more hardaxes of magnetization and one or more easy axes of magnetization in apredetermined plane. Along the easy axis, the material tends to exhibita higher coercivity and a highly non-linear relationship between appliedmagnetic field and magnetization, as previously described. This is incontrast with the hard axis which tends to exhibit lower coercivity andmaintain a relatively linear relationship between applied magnetic fieldand magnetization. This is generally illustrated in the graph 1000,which includes hysteresis loops for hard 1001 and soft 1002 axes.

Due to the low coercivity and linearity in magnetization, it isdesirable to utilize the hard axis for most applications. In the case ofan inductor, this would involve aligning the orientation of the hardaxis with the expected orientation of magnetic field lines thatoriginate from the inductor winding. The hard axis orientation can becontrolled by applying a DC magnetic field along the desired orientationof the easy axis during deposition or annealing. The magnitude of theapplied magnetic field should be of equal or greater magnitude than thesaturation field of the hard axis. The saturation field of the hardaxis, which is the magnetic field that saturates the magnetization alongthe hard axis, is the same as the induced anisotropy of the material.

Patterned magnetic cores, like those in the present invention, theinduced anisotropy must overcome the shape anisotropy, or demagnetizingfield (H_(shape)), in order for the magnetic core to maintain thedesired orientation of anisotropy. Shape anisotropy is determined by theshape of the patterned core. For thin cores, the magnitude of thedemagnetizing field can be approximated as:H _(shape) ≈M(N _(w) −N _(L))

where, M is the material's saturation magnetization, and N_(w)−N_(L) arethe patterned cores width and length, respectively. Thus, a core withhigh permeability will have low induced anisotropy, assuming constantsaturation magnetization. In applications where a high permeability isrequired, it may be difficult to achieve the desired orientation ofanisotropy for specific geometries where the shape anisotropy exceedsthe induced anisotropy.

Fabricating one or more embodiments entails deposition of magneticmaterial by electrodeposition, physical vapor deposition or othersuitable means. Layers are deposited onto the integrated circuit or aplanar substrate proximal to an electrically coupled integrated circuit.After deposition of the complete core of magnetic material, they arecovered with a masking layer that protects desired areas of the magneticcore. Other areas are left exposed so material may be selectivelyremoved by a wet chemical etch. This forging yields magnetic cores withspecific geometries that are transferred through the mask. A drychemical etch may remove the magnetic material, insulating and interfacelayers without much discrimination.

Another method for fabricating one or more embodiments, the substrate iscovered with a conductive seed layer that is deposited by physical vapordeposition. This seed layer is then covered with a photo-imageablepolymer masking layer that is not electrically conductive. Portions ofthe substrate where growth of the magnetic core is not desired arecoated with the polymer so that electrodeposition is conducted throughthe mask. This process yields magnetic cores with specific geometriesthat are transferred through the mask.

Fabrication can comprise depositing and patterning the magnetic cores byPVD and subtractive etching. This may also be performed byelectrodeposition through a non-conductive mask. The core then undergoesan oxidation process so that the exposed areas of the magnetic core areoxidized. Insulating oxide magnetic materials prevent electricalshorting between electrical connectors. The two different materialcompositions for the alternating layers are chosen so that differentelectrically insulating oxides are formed during the oxidation process.

FIG. 10 is a graphical abstraction 1000 of a magnetic anisotropicinductor under a saturation condition. As long as the inductor currentremains below the saturation current level, the inductance will stayrelatively constant with respect to inductor current. Inductor currentis depicted as being driven by a pulse width modulation (PWM) voltage,which is representative of a buck converter (power converter). The graph1000 plots magnetization (Tesla) versus magnetic field (Oersted).

FIG. 11 includes a graphical abstraction 1100 of a magnetic anisotropicinductor below a saturation current condition. The saturation current isthe inductor current level at which the magnetic core saturates alongthe inductor field direction. As long as the inductor current staysbelow the saturation current level the inductance will stay relativeconstant with respect to inductor current.

The graph 1100 plots inductor coil current versus time. The graph 1100illustrates the inductor current when driven by a PWM voltage, which isrepresentative of a buck converter (power converter). If an inductorcurrent exceeds the current, the effective relative magneticpermeability will go to 1, and the effective inductance will decreasesignificantly.

FIG. 11 also illustrates a graphical abstraction 1150 of bias coilcurrent versus time. As illustrated, the bias coil current is keptconstant to control the hard axis orientation of the magnetic core.

FIG. 12 includes a graphical abstraction 1200 of a magnetic anisotropicinductor above a saturation current condition. If the inductor currentexceeds the saturation current, the effective relative magneticpermeability will go to 1, and the effective inductance will decreasesignificantly. The graph 1200 plots inductor coil current versus time.

FIG. 12 also illustrates a graphical abstraction 1250 of bias coilcurrent versus time. As illustrated, the bias coil current is keptconstant to control the hard axis orientation of the magnetic core. Insome embodiments, the bias coil current is increased to avoid magneticsaturation by raising the effective saturation current limit.

FIG. 13 includes a graphical abstraction 1300 that illustrates thesaturation current increasing over time as the bias coil currentincreases. The graph 1300 plots inductor coil current versus time. FIG.13 also illustrates a graphical abstraction 1350 of bias coil currentversus time. The bias coil current is increased to raise the effectivesaturation current level, thus avoiding magnetic saturation.

Bias coil current is driven so that low frequency (DC) current isproportional to inductor coil current, and AC current is inverselyproportionally inductor coil current. AC current is superimposed ontothe bias coil. As such, the peak-to-peak inductor current ripple isreduced. Consequently, this has a similar effect of increasing theinductance value by raising the effective saturation limit.

The biasing coil may also be used to avoid magnetic saturation along thedirection of the inductor field/flux path in the described invention. Insome applications, the electrical current that passes through theinductor coil will have both an AC and DC component. In power conversionapplications, the DC component can be especially large in magnitude andmay be sufficient to saturate the magnetic core along the direction ofthe inductor. The inductor current that is sufficient to saturate themagnetic core is called the saturation current.

In the event of magnetic saturation, the effective relative permeabilityof the core is reduced to 1 (relative permeability of these materials istypically between 100 and 1500), which in turn causes the effectiveinductance to decrease. In order to avoid magnetic saturation, the biascoil current can be increased to raise the effective inductor coilsaturation current. The fields from the bias coil and the inductor coilwill be perpendicular to one another within the plane of the magneticcore, competing to magnetize the magnetic material along their fieldpath. This competition between the two magnetic fields prevents theinductor coil's magnetic field from saturating the magnetic core.

The biasing coil may also be used to increase the apparent inductance inthe device by generating an AC bias field that is superimposed upon theDC/low frequency bias field. Similar to the use case describedpreviously, where the bias coil field is used to avoid magneticsaturation, the current through the bias coil can be increased to avoidmagnetic saturation in the core. In addition to the DC/low frequencycurrent increasing, an AC current can be added that is opposite thecurrent traveling through the inductor coil. As the magnetic fields fromthe bias coil and inductor coil will be competing for magnetization ofthe core, decreasing the current that travels through the bias coil hasthe same effect upon the magnetization of the core as increasing thecurrent through the inductor coil.

Likewise, increasing the current that travels through the bias coil hasthe same effect upon the magnetization of the core as decreasing thecurrent through the inductor coil. The overall consequence is thatsuperposition of an AC current on the bias coil that is inverselyproportional to the inductor current will increase the apparentinductance observed by the inductor coil. Increasing this apparentinductance will result in either a smaller AC current through theinductor for a constant applied voltage, or a larger AC voltage acrossthe inductor terminals for a constant applied current.

FIG. 14 includes a graphical abstraction 1400 that illustrates thesaturation current increasing over time as the inductor coil currentincreases. The role of the bias coil and inductor coil can be switched,such that the inductor coil carries a current with the purpose ofbiasing the magnetic core such that the biasing coil will see afavorable change in inductance, hysteresis or both. Due to AC currentsuperimposed onto the bias coil, the peak-to-peak inductor currentripple is reduced. This can have a similar effect as increasing theinductance value.

FIG. 14 also illustrates a graphical abstraction 1450 of bias coilcurrent versus time. The bias coil current is driven so that lowfrequency (DC) current is proportional to inductor coil current, and ACcurrent is proportional but opposite to the inductor coil current.

In some embodiments, large current (e.g., greater than or equal to about10 mA depending on bias coil resistance) may be applied to the bias coilfor an extended period of time (e.g., greater than or equal to about 15minutes), so that the thermal energy dissipated in the bias coil canheat the magnetic film/core. The heat generated by the bias coil, incombination with time and the magnetic field originating from the biascoil can create conditions similar to those used during ahigh-temperature magnetic anneal (e.g., as described above) topermanently or semi-permanently fix the orientation of anisotropy forthe film/core. In this manner, the anisotropy of the magnetic film canbe controlled so that the hard axis orientation is parallel to themagnetic flux induced by the inductor coil, for the entire path of themagnetic flux.

FIG. 15 illustrates a method of operating an anisotropic inductor. Themethod includes 1501 inducing an easy axis in an anisotropic magneticcore lying in a core plane, the easy axis orthogonal to the core plane.The method also includes 1502 inducing a hard axis in the core, the hardaxis parallel to the core plane and/or the direction of the magneticfield. The method also includes 1503 generating a magnetic field with aninductor coil, the magnetic field parallel to the hard axis, theinductor coil wrapped around the core. In some embodiments, the easyaxis and the hard axis are disposed in the same plane.

In another aspect, the anisotropy of the magnetic core can be inducedduring deposition of the magnetic core material. A magnetic core havingdeposition-induced magnetic anisotropy can have improved magneticproperties (and thus improved performance of the inductor that includesthe deposition-induced anisotropic magnetic core) relative to magneticcores that have magnetic anisotropy induced after they are depositedand/or formed. For example, a deposition-induced anisotropic magneticcore can have reduced magnetic coercivity compared to magnetic coresthat have magnetic anisotropy induced after they are deposited and/orformed.

FIG. 21 is a flow chart 2100 of a method for fabricating an inductorhaving a deposition-induced magnetic anisotropy according to one or moreembodiments. In step 2101, a magnetic core is formed on a semiconductorsubstrate. The magnetic core comprises a ferromagnetic material, such asCo, Fe, or Ni, and/or any combination or alloy of these elements,potentially with other non-magnetic materials such as Ta, Zr, B, and/orP. While the magnetic core is being formed in step 2101, a bias magneticfield is generated in step 2102. The bias magnetic field passes throughthe magnetic core in a second direction. In step 2103, the bias magneticfield induces magnetic anisotropy in the magnetic core. For example, thebias magnetic field can induce an easy axis of magnetization in themagnetic core that is parallel to the bias magnetic field and/or that isparallel to the second direction. Inducement of the easy axis ofmagnetization can further induce a hard axis of magnetization in themagnetic core in a direction that is generally orthogonal to (e.g.,within about 10° of) the easy axis of magnetization.

In step 2104, an inductor coil is fabricated. The inductor coil windsaround the magnetic core formed in step 2101 such that the inductor coilcan generate an inductor magnetic field that passes through the magneticcore in a first direction that is orthogonal to the second direction.The inductor magnetic field and the hard axis of magnetization can bealigned (e.g., parallel to one another) in at least a portion of themagnetic core, and preferably for all or substantially all (e.g., atleast about 90%) of the magnetic core.

FIG. 22 is a flow chart 2100 of a method for forming adeposition-induced anisotropic magnetic core according to one or moreembodiments. In step 2201, a magnetic core material is deposited on asemiconductor substrate. The magnetic core material can comprise aferromagnetic material, for example as described herein. The magneticcore material can be deposited on a bottom conductor that forms aportion of the inductor coil. Alternatively, the magnetic core materialcan be deposited on a biasing coil that is formed above the bottomconductor. In either case, at least some insulating material is disposedbetween the magnetic core material and the underlying structure (e.g.,bottom conductor or biasing coil). The magnetic core material can bedeposited by physical vapor deposition (PVD) (including variants thereofsuch as ionized PVD (iPVD)) and/or PVD followed by electrodeposition.

In step 2202, a bias magnetic field is generated or produced while themagnetic core material is being deposited in step 2201. The biasmagnetic field is configured to pass through the magnetic core materialas it forms the magnetic core. For example, the bias magnetic field canbe generated during PVD of the magnetic core material and/or duringelectrodeposition of the magnetic core material. The bias magnetic fieldis configured to pass through the magnetic core in a second direction,for example as described above in step 2102. The bias magnetic field canbe generated by a bias coil formed on the same semiconductor substrateon which the bottom conductor is formed, on another semiconductorsubstrate, or on another location. In addition or in the alternative,the bias magnetic field can be generated by a permanent magnet formed onthe same semiconductor substrate on which the bottom conductor isformed. In some embodiments, the semiconductor substrate can be heatedduring step 2202 which can improve or enhance certain properties of thedeposited magnetic core material.

In step 2203, the bias magnetic field induces magnetic anisotropy in themagnetic core material as it is being deposited in step 2201, forexample as described above in step 2103. For example, the bias magneticfield can induce an easy axis of magnetization that is aligned with andsubstantially parallel to the direction that the bias magnetic fieldpasses through the magnetic core material. The bias magnetic field canbe configured to induce the easy axis of magnetization in the magneticcore material in a direction that is orthogonal to the direction throughwhich an inductor magnetic field, generated by an inductor coil thatwraps around the magnetic core (defined in the magnetic core material),will pass through the magnetic core. Inducement of the easy axis ofmagnetization in the magnetic core material can induce a hard axis ofmagnetization in a direction orthogonal to the easy axis ofmagnetization. The bias coil can be configured to induce the easy axisin a second direction such that the induced hard axis of magnetizationis aligned with and substantially parallel to the direction (e.g., afirst direction) that the inductor magnetic field will pass through themagnetic core. In the embodiments where the bias magnetic field isgenerated by a bias coil, the bias magnetic field can be turned offafter the magnetic core material is deposited.

In step 2204, a pattern is defined in the magnetic core material to forman anisotropic magnetic core. The pattern can be defined by depositingand patterning a photo-imageable material, such as photoresist, andetching the underlying magnetic core material according to the patternedphoto-imageable material. The pattern can also be defined by depositingthe magnetic material through a shadow mask, a masking substrate withopenings, that is physically placed on the wafer during film deposition.Those of skill in the art will recognize that there may be otherfabrication techniques to define a pattern in the magnetic corematerial.

In some embodiments, the shadow mask can be comprised of a permanentmagnet and/or a bias coil that induces a desired anisotropy in themagnetic core material during deposition. As such, steps 2203 and 2204can be combined in these embodiments. The magnetic fields generated bythe permanent magnet and/or by the bias coil in the shadow mask canfunction the same as or similar to the bias magnetic field describedabove. For example, the magnetic fields generated by the permanentmagnet and/or the bias coil in the shadow mask can be configured toinduce an easy axis of magnetization in the magnetic core material inthe second direction that is orthogonal to the direction through whichthe inductor magnetic field will pass. Inducement of the easy axis ofmagnetization in the magnetic core material can induce a hard axis ofmagnetization in a direction orthogonal to the easy axis ofmagnetization. The induced hard axis of magnetization can be alignedwith and substantially parallel to the direction (e.g., a firstdirection) that the inductor magnetic field will pass through themagnetic core.

In some embodiments, steps 2101-2103 in flow chart 2100 can be performedaccording to flow chart 2200.

FIG. 23 is a cross-sectional view of a semiconductor structure 2300 toillustrate a first step for fabricating an inductor that includes adeposition-induced anisotropic magnetic core according to one or moreembodiments. The cross section in FIG. 23 is taken through a planeorthogonal to core plane 625. In FIG. 23, a bottom conductor 2310 isdeposited and patterned on a semiconductor substrate 2320. The bottomconductor 2310 is formed in an insulating material 2330 such aspolyimide, polybenzoxazole (PBO), SU-8 photoresist, SiO₂ and/or SiN. Insome embodiments, the bottom conductor 2310 can be formed using knownsemiconductor fabrication techniques. The bottom conductor 2310 cancomprise copper and/or aluminum, an alloy of copper and/or aluminum, oranother conductive material.

FIG. 24 is a cross-sectional view of the semiconductor structure 2300 toillustrate a second step for fabricating an inductor that includes adeposition-induced anisotropic magnetic core according to one or moreembodiments. In FIG. 24, a bias coil 2340 is deposited and patterned onthe bottom conductor 2310. However, some insulating material 2330 isdisposed between the bias coil 2340 and the bottom conductor 2310 toprevent electrical conduction/shorting therebetween. In someembodiments, the bias coil 2340 can be formed using known semiconductorfabrication techniques. The bias coil 2340 comprises a conductivematerial that can be the same as or different than the material(s) thatcomprise the bottom conductor 2310. The bias coil 2340 is configured andarranged to produce a bias magnetic field that will pass through themagnetic core material in a direction that is orthogonal to thedirection that the inductor coil will pass through the magnetic core.

FIG. 25 is a cross-sectional view of the semiconductor structure 2300 toillustrate a third step for fabricating an inductor that includes adeposition-induced anisotropic magnetic core according to one or moreembodiments. In FIG. 25, the bias coil 2340 produces a bias magneticfield 2345 as magnetic core material is deposited 2500 from a depositionsource 2510. The deposition source 2510 can be a PVD manufacturing tool,an electroplating (or electrodeposition) manufacturing tool, a chemicalvapor deposition manufacturing tool, or other semiconductormanufacturing tool. As discussed above, the bias coil 2340 is configuredand arranged to produce the bias magnetic field 2345 through themagnetic core material, during deposition thereof, in a direction thatis orthogonal to the direction that the inductor coil will pass throughthe magnetic core material (and magnetic core). The bias coil 2340 canproduce or generate the bias magnetic field 2345 when current flows inthe bias coil 2340. For example, each bias coil 2340 across the wafercan be connected to common positive and negative terminals thatinterface with terminals on the wafer chuck, in the deposition chamberfor the magnetic core material, around the edge of the wafer.Alternatively, bias coil 2340 can comprise or can be replaced with abias permanent magnet 4040 that can generate a bias permanent magneticfield 4045 without flowing current in the bias coil 2340, as illustratedin semiconductor structure 4000 in FIG. 40. The bias permanent magneticfield 4045 can function the same as or substantially the same as biasmagnetic field 2345.

FIG. 26 is a cross-sectional view of the semiconductor structure 2300 tofurther illustrate the third step for fabricating an inductor thatincludes a deposition-induced anisotropic magnetic core according to oneor more embodiments. In FIG. 26, magnetic core material 2600 has beendeposited from deposition source 2510 while being exposed to the biasmagnetic field 2345. The bias magnetic field 2345 induces an easy axisof magnetization 2610 in the magnetic core material 2600 in a directionparallel to the bias magnetic field 2345 as it passes through themagnetic core material 2600. In the embodiments where the bias magneticfield 2345 is generated by bias coil 2340, the bias magnetic field 2345can be turned off after the magnetic core material 2600 is deposited.

FIG. 27 is a cross-sectional view of the semiconductor structure 2300 toillustrate a fourth step for fabricating an inductor that includes adeposition-induced anisotropic magnetic core according to one or moreembodiments. In FIG. 27, the magnetic core material 2600 has beendeposited and patterned to form a magnetic core 2700 having a shape,which can be a toroid or other shape (e.g., as discussed herein). Asdiscussed above, the bias magnetic field 2600 induced the magnetic corematerial 2600 to become magnetically anisotropic. Specifically, the biasmagnetic field 2345 induced the easy axis of magnetization 2610 in themagnetic core material 2600. Inducing the easy axis of magnetization2610 further induces a hard axis of magnetization 2710 in a directionorthogonal to the easy axis of magnetization 2610. For example, the hardaxis of magnetization 2710 is oriented into the page in magnetic coreportion 2700A and out of the page in magnetic core portion 2700B.

FIG. 28 is a cross-sectional view of the semiconductor structure 2300 toillustrate a fifth step for fabricating an inductor that includes adeposition-induced anisotropic magnetic core according to one or moreembodiments. In FIG. 28, a top conductor 2810 is formed above themagnetic core 2700. The top conductor 2810 can comprise the same ordifferent conductive material as bottom conductor 2310 or bias coil2340. In addition, conductive VIAs 2820 electrically connect the bottomand top conductors 2310, 2810 to form an inductor coil 2800 that windsaround the magnetic core 2700. The top conductor 2810 and the conductiveVIAs are formed in additional insulating material 2330. The inductorcoil 2800 is configured and arranged so that, when current flowstherein, the inductor coil 2800 produces an inductor magnetic field 2830that is substantially parallel to (e.g., within about 10° of) andaligned with the hard axis of magnetization 2710 of the magnetic corematerial 2600. The inductor coil 2800 and magnetic core 2700 form aninductor 2840. The fully-fabricated semiconductor structure 3000including inductor 2840 that includes the deposition-induced anisotropicmagnetic core 2700 is illustrated in FIG. 28.

Therefore, the inductor coil 2800 is configured and arranged to producethe inductor magnetic field 2830 that passes through the magnetic core2700 (e.g., through the magnetic core material 2600) in a firstdirection. The bias coil 2340 is configured and arranged to produce thebias magnetic field 2345 that passes through the magnetic core 2700(e.g., through the magnetic core material 2600) during its deposition ina second direction that is orthogonal to the first direction. The biasmagnetic field 2345 induces the magnetic core material 2600 tosubstantially align its easy axis of magnetization 2610 with the biasmagnetic field 2345 such that the easy axis of magnetization 2610 issubstantially parallel to the second direction. Inducement of the easyaxis of magnetization 2610 in the second direction causes the magneticcore material 2600 to substantially align its hard axis of magnetization2710 in a direction orthogonal to the second direction. The biasmagnetic field 2345 can be configured to orient the easy axis ofmagnetization 2610 such that the magnetic core material 2600 aligns itshard axis of magnetization 2710 to be substantially parallel to andaligned with the second direction and to the inductor magnetic field2830.

In some embodiments, the deposition-induced magnetic anisotropy of themagnetic core 2700 can have improved magnetic properties (and thusimproved performance of the inductor 2840) relative to magnetic coresthat have magnetic anisotropy induced after they are deposited and/orformed. For example, magnetic core 2700 has a reduced magneticcoercivity compared to magnetic cores that have magnetic anisotropyinduced after they are deposited and/or formed.

FIG. 29 is a flow chart 2900 of a method for fabricating an inductorthat includes a deposition-induced anisotropic magnetic core accordingto one or more embodiments. The flow chart 2900 can correspond to FIGS.23-28, described above.

In step 2901, a bottom conductor is formed on a semiconductor substrate.For example, the bottom conductor (e.g., bottom conductor 2310) can beformed as discussed above in FIG. 23. The bottom conductor can be formeddirectly on the semiconductor substrate or indirectly on thesemiconductor substrate. For example, the bottom conductor can be formedon a semiconductor structure that itself is formed directly on thesemiconductor substrate.

In step 2902, a bias coil is formed over the bottom conductor. Forexample, the bias coil (e.g., bias coil 2340) can be formed as discussedabove in FIG. 24. An insulating material (e.g., insulating material2330) is disposed between the bottom conductor and the bias coil toprevent electrical conduction/shorting therebetween.

In step 2903, a deposition-induced anisotropic magnetic core is formed.For example, the deposition-induced anisotropic magnetic core (e.g.,magnetic core 2700) can be formed as discussed above in FIGS. 25-27.

In step 2904, a top conductor and VIAs that electrically connect thebottom and top conductors are fabricated. For example, the top conductorand VIAs (e.g., top conductor 2810 and VIAs 2820) can be formed asdiscussed above in FIG. 28. The bottom conductor, the top conductor, andthe VIAs form an inductor coil (e.g., inductor coil 2800) that is woundor wrapped around the deposition-induced anisotropic magnetic core. Aninductor (e.g., inductor 2840) that includes a deposition-inducedanisotropic magnetic core is formed upon completion of step 2904 in flowchart 2900.

FIG. 30 is a cross-sectional view of a semiconductor structure 3000 toillustrate an alternative embodiment for fabricating an inductor thatincludes a deposition-induced anisotropic magnetic core. In FIG. 30, thebias coil 2340 is formed below the bottom conductor 2310, in contrast tosemiconductor structure 2300 (e.g., FIG. 24) where the bias coil 2340 isformed above the bottom conductor 2310. Thus in FIG. 30 the bias coil2340 is disposed between the bottom conductor 2310 and the semiconductorsubstrate 2320. Alternatively, the bias coil 2340 can comprise or can bereplaced with a bias permanent magnet 4140 that can generate a biaspermanent magnetic field 4145 without flowing current in the bias coil2340, as illustrated in semiconductor structure 4100 in FIG. 41. Thebias permanent magnetic field 4145 can function the same as orsubstantially the same as bias magnetic field 3045.

Regardless of whether the bias coil 2340 is disposed above or below thebottom conductor 2310 (e.g., as illustrated in FIGS. 24 and 30,respectively), (a) the bias coil 2340 and (b) the magnetic core to beformed out of magnetic core material 2600 (e.g., a target location forthe magnetic core) and/or the bottom conductor 2310 can be alignedhorizontally within about 200 μm of each other, including about 150 μm,about 100 μm, about 50 μm, and/or about 20 μm, including any value orrange between any two of the foregoing.

The fabrication of the inductor otherwise follows flow chart 2900 andFIGS. 25-28. For example, the bias coil 2340 can produce a bias magneticfield 3045, during deposition of the magnetic core material 2600, toinduce magnetic anisotropy in the magnetic core material 2600. Forexample, the bias magnetic field 3045 induces an easy axis ofmagnetization 2610 in the magnetic core material 2600 that is alignedwith and substantially parallel to the bias magnetic field 3045 as itpasses through the magnetic core material 2600. The fully-fabricatedsemiconductor structure 3000 including an inductor 3030 that includesthe deposition-induced anisotropic magnetic core 2700 is illustrated inFIG. 31.

Therefore, the inductor coil 2800 is configured and arranged to producethe inductor magnetic field 2830 that passes through the magnetic core2700 (e.g., through the magnetic core material 2600) in a firstdirection. The bias coil 2340 is configured and arranged to produce thebias magnetic field 3045 that passes through the magnetic core 2700(e.g., through the magnetic core material 2600) during its deposition ina second direction that is orthogonal to the first direction. The biasmagnetic field 3045 induces the magnetic core material 2600 to align itseasy axis of magnetization 2610 with the bias magnetic field 3045 suchthat the easy axis of magnetization 2610 is substantially parallel tothe second direction. Inducement of the easy axis of magnetization 2610in the second direction causes the magnetic core material 2600 to alignits hard axis of magnetization 2710 in a direction orthogonal to thesecond direction. The bias magnetic field 3045 can be configured toorient the easy axis of magnetization 2610 such that the magnetic corematerial 2600 aligns its hard axis of magnetization 2710 to besubstantially parallel to the second direction and to the inductormagnetic field 2830.

FIG. 32 is a flow chart 3200 of a method for fabricating an inductorthat includes a deposition-induced anisotropic magnetic core accordingto an alternative embodiment.

In step 3201, a bias coil is formed on a semiconductor substrate. Forexample, the bias coil (e.g., bias coil 2340) can be formed as discussedabove in FIGS. 24 and 30. The bias coil can be formed directly on thesemiconductor substrate or indirectly on the semiconductor substrate.For example, the bias coil can be formed on a semiconductor structurethat itself is formed directly on the semiconductor substrate.

In step 3202, a bottom conductor is formed over the bias coil. Forexample, the bottom conductor (e.g., bottom conductor 2310) can beformed as discussed above in FIGS. 23 and 30. An insulating material(e.g., insulating material 2330) is disposed between the bias coil andthe bottom conductor to prevent electrical conduction/shortingtherebetween.

Steps 2903 and 2904 in flow chart 3200 proceed as described above inflow chart 2200. An inductor (e.g., inductor 3040) that includes adeposition-induced anisotropic magnetic core is formed upon completionof step 2904 in flow chart 3200.

FIG. 33 is a cross-sectional view of an assembly 3300 to illustrateanother alternative embodiment for fabricating an inductor that includesa deposition-induced anisotropic magnetic core. In FIG. 33, the biascoil 2340 is disposed below a second substrate 3320. Thus in FIG. 33substrates 2320 and 3320 are disposed between the bias coil 2340 and thebottom conductor 2310. The substrates 2320, 3320 are positioned relativeto each other so that a bias magnetic field 3345, produced by the biascoil 2340 on the second substrate 3320, can pass through the magneticcore material 2600 in a second direction to induce the easy axis ofmagnetization 2610 in the magnetic core material 2600 to besubstantially parallel to the second direction.

The fabrication of the inductor otherwise follows flow chart 2900 andFIGS. 25-28. For example, the bias coil 2340 produces the bias magneticfield 3345, during deposition of the magnetic core material 2600, toinduce magnetic anisotropy in the magnetic core material 2600. The biasmagnetic field 3345 induces an easy axis of magnetization 2610 in themagnetic core material 2600 that is aligned with and substantiallyparallel to the bias magnetic field 3345 as it passes through themagnetic core material 2600. The fully-fabricated semiconductorstructure 3400 including an inductor 3430 that includes thedeposition-induced anisotropic magnetic core 2700 is illustrated in FIG.34.

Therefore, the inductor coil 2800 is configured and arranged to producethe inductor magnetic field 2830 that passes through the magnetic core2700 (e.g., through the magnetic core material 2600) in a firstdirection. The bias coil 2340 is configured and arranged to produce thebias magnetic field 3345 that passes through the magnetic core 2700(e.g., through the magnetic core material 2600) during its deposition ina second direction that is orthogonal to the first direction. The biasmagnetic field 3345 induces the magnetic core material 2600 to align itseasy axis of magnetization 2610 with the bias magnetic field 3345 suchthat the easy axis of magnetization 2610 is substantially parallel tothe second direction. Inducement of the easy axis of magnetization 2610in the second direction causes the magnetic core material 2600 to alignits hard axis of magnetization 2710 in a direction orthogonal to thesecond direction. The bias magnetic field 3345 can be configured toorient the easy axis of magnetization 2610 such that the magnetic corematerial 2600 aligns its hard axis of magnetization 2710 to besubstantially parallel to the second direction and to the inductormagnetic field 2830. The first and second 2320, 3320 can be separatedafter the deposition-induced magnetic core material is deposited. Thesecond substrate 3320 can include a semiconductor material (e.g.,silicon) or a non-semiconductor material such as glass, ceramic, metal,or polymer.

FIG. 35 is a flow chart 3200 of a method for fabricating an inductorthat includes a deposition-induced anisotropic magnetic core accordingto an alternative embodiment. In step 3501, a bias coil is formed on asecond substrate. For example, the bias coil (e.g., bias coil 2340) canbe formed as discussed above in FIGS. 24 and 30. The bias coil can beformed directly or indirectly on the second substrate. For example, thebias coil can be formed on a structure that itself is formed directly onthe second substrate. The second substrate can include a semiconductormaterial (e.g., silicon) or a non-semiconductor material such as glass,ceramic, metal, or polymer.

In step 3202, a bottom conductor is formed on a first semiconductorsubstrate. For example, the bottom conductor (e.g., bottom conductor2310) can be formed as discussed above in FIGS. 23 and 30. An insulatingmaterial (e.g., insulating material 2330) can be disposed between thebottom conductor and the first semiconductor substrate (or underlyinglayer such as in a semiconductor structure disposed on the firstsemiconductor substrate) to prevent electrical conduction/shortingtherebetween.

In step 3503, the first and second substrates are positioned and alignedrelative to one another (e.g., as discussed herein) such that the biasmagnetic field generated by the bias coil will pass through the magneticcore material, during deposition thereof, in a direction that isorthogonal to the direction that the inductor coil will pass through themagnetic core. For example, the first and second substrates can bepositioned relative to each other so that a bias magnetic field,produced by the bias coil on the second substrate 3320 can pass throughthe magnetic core material, during deposition thereof, in a firstdirection. Positioning the first and second substrates can includemoving the first and/or the second semiconductor substrate(s) relativeto the other. In some embodiments, the first and second substrates arepositioned so they are in contact with each other (e.g., a major portionof each substrate is in contact with the other).

Steps 2903 and 2904 in flow chart 3500 proceed as described above inflow chart 2900. An inductor (e.g., inductor 3040) that includes adeposition-induced anisotropic magnetic core is formed upon completionof step 2904 in flow chart 3500. Following step 2903 or 2904, the firstand second substrates can be separated.

FIG. 36 is a cross-sectional view of an assembly 3600 to illustrate yetanother alternative embodiment for fabricating an inductor that includesa deposition-induced anisotropic magnetic core. Assembly 3600 is thesame as assembly 3300 except that the bias coil 2340 is disposed abovethe second semiconductor substrate 3320.

The fabrication of the inductor using assembly 3600 follows flow chart3500. For example, the bias coil 2340 produces a bias magnetic field3645, during deposition of the magnetic core material 2600, to inducemagnetic anisotropy in the magnetic core material 2600. The biasmagnetic field 3645 induces an easy axis of magnetization 2610 in themagnetic core material 2600 that is aligned with and substantiallyparallel to the bias magnetic field 3645 as it passes through themagnetic core material 2600. The fully-fabricated semiconductorstructure including an inductor that includes the deposition-inducedanisotropic magnetic core is the same as the semiconductor structure3400 illustrated in FIG. 34.

Regardless of whether the bias coil 2340 is disposed below or above thesecond substrate 3320 (e.g., as illustrated in FIGS. 33 and 36,respectively), (a) the bias coil 2340 and (b) the magnetic core to beformed out of magnetic core material 2600 (e.g., a target location forthe magnetic core) and/or the bottom conductor 2310 can be alignedhorizontally within about 200 μm of each other, including about 150 μm,about 100 μm, about 50 μm, and/or about 20 μm, including any value orrange between any two of the foregoing. In addition or in thealternative, (a) the bias coil 2340 and (b) the magnetic core to beformed out of magnetic core material 2600 (e.g., a target location forthe magnetic core) and/or the bottom conductor 2310 can be alignedvertically within about 4 mm of each other, including about 3 mm, about2 mm, and/or about 1 mm.

The first and second substrates 2320, 3320 can be separated after thedeposition-induced magnetic core material is deposited.

FIG. 37 is a cross-sectional view of an assembly 3700 to illustrateanother alternative embodiment for fabricating an inductor that includesa deposition-induced anisotropic magnetic core. In FIG. 37, biaspermanent magnets 3740 are disposed below a second substrate 3720 suchthat the substrates 2320 and 3720 are disposed between the biaspermanent magnets 3740 and the bottom conductor 2310. The substrates2320, 3720 are positioned relative to each other so that bias permanentmagnetic fields 3745, produced by the bias permanent magnets 3740 on thesecond substrate 3720, can pass through the magnetic core material 2600in a second direction to induce the easy axis of magnetization 2610 inthe magnetic core material 2600 to be substantially parallel to thesecond direction. The second substrate 3720 can include a semiconductormaterial (e.g., silicon) or a non-semiconductor material such as glass,ceramic, metal, or polymer.

The fabrication of the inductor otherwise follows flow chart 2900 andFIGS. 25-28. For example, the bias permanent magnets 3740 produce thebias permanent magnetic fields 3345, during deposition of the magneticcore material 2600, to induce magnetic anisotropy in the magnetic corematerial 2600. The bias permanent magnetic fields 3345 induce an easyaxis of magnetization 2610 in the magnetic core material 2600 that isaligned with and substantially parallel to the bias permanent magneticfield 3345 as it passes through the magnetic core material 2600. Thefully-fabricated semiconductor structure is the same as thefully-fabricated semiconductor structure 3400, including an inductor3430 that includes the deposition-induced anisotropic magnetic core2700, illustrated in FIG. 34. The first and second substrates 2320, 3720can be separated after the deposition-induced magnetic core material isdeposited.

FIG. 38 is a cross-sectional view of an assembly 3800 to illustrate yetanother alternative embodiment for fabricating an inductor that includesa deposition-induced anisotropic magnetic core. Assembly 3800 is thesame as assembly 3700 except that the bias permanent magnets 3740 aredisposed above the second substrate 3720.

Regardless of whether the bias permanent magnets 3740 are disposed belowor above the second substrate 3720 (e.g., as illustrated in FIGS. 37 and38, respectively), (a) the bias permanent magnets 3740 and (b) themagnetic core to be formed out of magnetic core material 2600 (e.g., atarget location for the magnetic core) and/or the bottom conductor 2310can be aligned horizontally within about 200 μm of each other, includingabout 150 μm, about 100 μm, about 50 μm, and/or about 20 μm, includingany value or range between any two of the foregoing. In addition or inthe alternative, (a) the bias permanent magnets 3740 and (b) themagnetic core to be formed out of magnetic core material 2600 (e.g., atarget location for the magnetic core) and/or the bottom conductor 2310can be positioned vertically within a predetermined distance of eachother such as about 4 mm of each other, including about 3 mm, about 2mm, and/or about 1 mm.

FIG. 39 is a flow chart 3900 of a method for fabricating an inductorthat includes a deposition-induced anisotropic magnetic core usingpermanent magnets according to an alternative embodiment. In step 3701,permanent magnets (e.g., bias permanent magnets 3740) are formed on asecond substrate. The permanent magnets can be formed directly orindirectly on the second substrate. For example, the permanent magnetscan be formed on a structure that itself is formed directly on thesecond substrate. The second substrate can include a semiconductormaterial (e.g., silicon) or a non-semiconductor material such as glass,ceramic, metal, or polymer.

Flow chart 3900 is otherwise identical to flow chart 3500. Followingstep 2903 or 2904, the first and second substrates can be separated.

In one or more of the methods for fabricating an inductor that includesa deposition-induced anisotropic magnetic core, the method(s) caninclude heating the substrate on which the deposition-inducedanisotropic magnetic core is to be formed to a temperature of about 150°C. to about 250° C., including about 175° C., 200° C., 225° C., or anytemperature or temperature range between any two of the foregoingtemperatures. This heating can occur during deposition of the magneticcore material. In some embodiments, the heating can reduce the magneticcoercivity of the deposition-induced anisotropic magnetic core.

The present invention is designed to be easily integrated withcomplementary metal oxide semiconductor (CMOS) and integrated circuitchip fabrication. However, other scale and methods of manufacture arenot beyond the scope of the present invention.

The embodiments described and illustrated herein are not meant by way oflimitation, and are rather exemplary of the kinds of features andtechniques that those skilled in the art might benefit from inimplementing a wide variety of useful products and processes. Forexample, in addition to the applications described in the embodimentsabove, those skilled in the art would appreciate that the presentdisclosure can be applied to other applications.

The present invention should not be considered limited to the particularembodiments described above, but rather should be understood to coverall aspects of the invention as fairly set out herein. Variousmodifications, equivalent processes, as well as numerous structures towhich the present invention may be applicable, will be readily apparentto those skilled in the art to which the present invention is directedupon review of the present disclosure.

What is claimed is:
 1. A method of fabricating an inductor, the methodcomprising: depositing a ferromagnetic material on a substrate; defininga pattern in the ferromagnetic material to form a ferromagnetic core onthe substrate, the ferromagnetic core lying in a core plane; fabricatingan inductor coil that winds around the ferromagnetic core, the inductorcoil configured to generate an inductor magnetic field that passesthrough the ferromagnetic core in a first direction parallel to the coreplane; and while depositing the ferromagnetic material: generating abias magnetic field that passes through the ferromagnetic material in asecond direction that is orthogonal to the first direction; and inducinga magnetic anisotropy in the ferromagnetic material with the biasmagnetic field, wherein inducing the magnetic anisotropy furthercomprises: with the bias magnetic field, inducing an easy axis ofmagnetization in the ferromagnetic material, the easy axis parallel tothe second direction, and inducing a hard axis of magnetization in theferromagnetic material, the hard axis orthogonal to the easy axis. 2.The method of claim 1, wherein the hard axis is parallel to the firstdirection.
 3. The method of claim 1, further comprising, whiledepositing the ferromagnetic material, applying current in a bias coildisposed on the substrate to generate the bias magnetic field.
 4. Themethod of claim 3, further comprising applying at least 10 mA of currentin the bias coil.
 5. The method of claim 3, further comprisingfabricating the bias coil on the substrate, the bias coil disposedparallel to the core plane.
 6. The method of claim 5, further comprisingdisposing the bias coil between the ferromagnetic core and thesubstrate.
 7. The method of claim 6, further comprising disposing thebias coil between the inductor coil and the substrate.
 8. The method ofclaim 6, wherein the inductor coil includes a top conductor, a bottomconductor, and a VIA that is electrically coupled to the top and bottomconductors, and the method further comprises disposing the bias coilbetween the ferromagnetic core and the bottom conductor.
 9. The methodof claim 5, further comprising aligning an axis of symmetry of the biascoil with a target axis of symmetry of the ferromagnetic core.
 10. Themethod of claim 1, wherein the ferromagnetic core is formed on a firstsubstrate and the method further comprises: providing relative movementbetween the first substrate and a second substrate having a bias coildisposed thereon such that the bias coil on the second substrate and atarget location for the ferromagnetic core on the first substrate arewithin a predetermined distance of one another; and generating the biasmagnetic field with the bias coil.
 11. The method of claim 10, furthercomprising applying current in the bias coil to generate the biasmagnetic field.
 12. The method of claim 11, further comprising applyingat least 10 mA of current in the bias coil.
 13. The method of claim 10,wherein the relative movement between the first substrate and the secondsubstrate results in a relative positioning thereof in which the firstsubstrate and the second substrate are in contact with one another. 14.The method of claim 10, wherein the relative movement between the firstsubstrate and the second substrate aligns the bias coil and a targetlocation for the ferromagnetic core.
 15. The method of claim 1, whereinthe ferromagnetic material is deposited on a semiconductor substrate.16. The method of claim 1, wherein the ferromagnetic core is formed on asemiconductor substrate.
 17. A method of fabricating an inductor, themethod comprising: depositing a ferromagnetic material on a substrate;defining a pattern in the ferromagnetic material to form a ferromagneticcore on the substrate, the ferromagnetic core lying in a core plane;fabricating an inductor coil that winds around the ferromagnetic core,the inductor coil configured to generate an inductor magnetic field thatpasses through the ferromagnetic core in a first direction parallel tothe core plane; and while depositing the ferromagnetic material:generating a bias magnetic field that passes through the ferromagneticmaterial in a second direction that is orthogonal to the firstdirection; inducing a magnetic anisotropy in the ferromagnetic materialwith the bias magnetic field; and while depositing the ferromagneticmaterial, applying current in a bias coil disposed on the substrate togenerate the bias magnetic field.
 18. The method of claim 17, whereininducing the magnetic anisotropy further comprises inducing a hard axisof magnetization in the ferromagnetic material, the hard axis orthogonalto the easy axis.
 19. The method of claim 18 wherein the hard axis isparallel to the first direction.
 20. The method of claim 17, furthercomprising applying at least 10 mA of current in the bias coil.
 21. Themethod of claim 17, further comprising fabricating the bias coil on thesubstrate, the bias coil disposed parallel to the core plane.
 22. Themethod of claim 21, further comprising disposing the bias coil betweenthe ferromagnetic core and the substrate.
 23. The method of claim 22,further comprising disposing the bias coil between the inductor coil andthe substrate.
 24. The method of claim 22, wherein the inductor coilincludes a top conductor, a bottom conductor, and a VIA that iselectrically coupled to the top and bottom conductors, and the methodfurther comprises disposing the bias coil between the ferromagnetic coreand the bottom conductor.
 25. The method of claim 21, further comprisingaligning an axis of symmetry of the bias coil with a target axis ofsymmetry of the ferromagnetic core.
 26. The method of claim 17, whereinthe ferromagnetic material is deposited on a semiconductor substrate.27. The method of claim 17, wherein the ferromagnetic core is formed ona semiconductor substrate.
 28. A method of fabricating an inductor, themethod comprising: depositing a ferromagnetic material on a substrate;defining a pattern in the ferromagnetic material to form a ferromagneticcore on the substrate, the ferromagnetic core lying in a core plane;fabricating an inductor coil that winds around the ferromagnetic core,the inductor coil configured to generate an inductor magnetic field thatpasses through the ferromagnetic core in a first direction parallel tothe core plane; and while depositing the ferromagnetic material:generating a bias magnetic field that passes through the ferromagneticmaterial in a second direction that is orthogonal to the firstdirection; and inducing a magnetic anisotropy in the ferromagneticmaterial with the bias magnetic field, wherein the ferromagnetic core isformed on a first substrate and the method further comprises: providingrelative movement between the first substrate and a second substratehaving a bias coil disposed thereon such that the bias coil on thesecond substrate and a target location for the ferromagnetic core on thefirst substrate are within a predetermined distance of one another; andgenerating the bias magnetic field with the bias coil.
 29. The method ofclaim 28, wherein inducing the magnetic anisotropy further comprisesinducing a hard axis of magnetization in the ferromagnetic material, thehard axis orthogonal to the easy axis.
 30. The method of claim 28,wherein the hard axis is parallel to the first direction.
 31. The methodof claim 28, further comprising applying current in the bias coil togenerate the bias magnetic field.
 32. The method of claim 31, furthercomprising applying at least 10 mA of current in the bias coil.
 33. Themethod of claim 28, wherein the relative movement between the firstsubstrate and the second substrate results in a relative positioningthereof in which the first substrate and the second substrate are incontact with one another.
 34. The method of claim 28, wherein therelative movement between the first substrate and the second substratealigns the bias coil and a target location for the ferromagnetic core.35. The method of claim 28, wherein the ferromagnetic material isdeposited on a semiconductor substrate.
 36. The method of claim 28,wherein the ferromagnetic core is formed on a semiconductor substrate.